Pyrotechnic linear inflator

ABSTRACT

An airbag inflator ( 10 ) including an elongated outer housing ( 12 ) having an interior and one or more orifices ( 22 ) formed therealong to enable fluid communication between the outer housing interior and an exterior of the outer housing ( 12 ). The outer housing orifice(s) ( 22 ) open from the outer housing interior toward a first side (F) of the inflator. An elongated inner housing ( 14 ) is positioned in the outer housing interior. The inner housing ( 14 ) has an interior and one or more orifices ( 20 ) formed therealong to enable fluid communication between the inner housing interior and an exterior of the inner housing ( 14 ). The inner housing orifice(s) ( 20 ) open from the inner housing interior toward a second side (S) of the inflator. A quantity of a gas generant composition ( 16 ) extends along a portion of the interior of the inner housing ( 14 ). The gas generant ( 16 ) has a substantially “C”-shaped cross-section with a slot ( 24 ) extending along the length of the gas generant ( 16 ). The gas generant slot ( 24 ) is oriented facing the inner housing orifice(s) ( 20 ). A filter ( 15 ) is positioned intermediate the inner housing orifice(s) ( 20 ) and the outer housing orifice(s) ( 22 ) for filtering combustion products generated by combustion of the gas generant composition ( 16 ). An igniter ( 40 ) is operatively coupled to the gas generant composition ( 16 ) so as to enable fluid communication between the igniter ( 40 ) and the gas generant composition ( 16 ) upon activation of the inflator ( 10 ). The slotted, “C”-shaped cross section of the gas generant ( 16 ) provides a greater exposed gas generant surface area than would be achievable without the slot ( 24 ). This enhances the ignition and burning of the gas generant composition ( 16 ) upon inflator activation.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of provisional application Ser. No.60/519,880, filed on Nov. 13, 2003.

BACKGROUND OF THE INVENTION

The present invention relates to inflators for vehicle airbags and, moreparticularly, to a linear inflator which discharges inflation gas alongthe length of the inflator for use in side impact or head curtain airbagsystems.

Typical side impact or head curtain airbag modules use one or morestandard airbag inflators discharging into a distribution pipe fordelivering the gas to the bag. There are pressure losses associated withgas flow through the distribution pipe, resulting in lower systemefficiencies. In addition, extra space inside the vehicle is required tohouse the inflator portion of the devices.

SUMMARY OF THE INVENTION

In accordance with the present invention, an airbag inflator is providedwhich includes an elongated outer housing having an interior and one ormore orifices to enable fluid communication between the outer housinginterior and an exterior of the outer housing. The outer housingorifice(s) open from the outer housing interior toward a first side ofthe inflator. An elongated inner housing is positioned in the outerhousing interior. The inner housing has an interior and one or moreorifices to enable fluid communication between the inner housinginterior and an exterior of the inner housing. The inner housingorifice(s) open from the inner housing interior toward a second side ofthe inflator. A quantity of a gas generant composition extends along aportion of the interior of the inner housing. The gas generant has asubstantially “C”-shaped cross-section with a slot extending along thelength of the gas generant. The gas generant slot is oriented facing theinner housing orifice(s). A filter is positioned intermediate the innerhousing orifice(s) and the outer housing orifice(s) for filteringcombustion products generated by combustion of the gas generantcomposition. An igniter is operatively coupled to the gas generantcomposition so as to enable fluid communication between the igniter andthe gas generant composition upon activation of the inflator.

Upon a crash event, a signal from a crash sensor is conveyed to theigniter, thereby activating the igniter and igniting gas generant.Inflation gas produced by combustion of the gas generant proceeds out ofthe inner housing orifice(s) and flows around either side of the innerhousing and also through the filter. The inflation gas then exits theinflator via the outer housing orifice(s) to inflate the airbag.

The slotted, “C”-shaped cross section of the gas generant provides agreater exposed gas generant surface area than would be achievablewithout the slot. This enhances the ignition and burning of the gasgenerant composition upon inflator activation, while also providingfluid communication between a relatively large surface area of gasgenerant and the inner housing orifice(s). The present inflator is alsoself-contained, generating and discharging gas uniformly along itslength without the need for a separate conventional inflator connectedto a distribution pipe. This reduces the overall size envelope of theinflator. The inflator of the present invention is also lower in costand simpler to manufacture than many known designs.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional end view of one embodiment of an inflator inaccordance with the present invention;

FIG. 2 is a cross-sectional side view of the embodiment of the inflatorshown in FIG. 1;

FIG. 2A is a cross-sectional side view of an embodiment of an igniterassembly incorporated into the inflator of the present invention;

FIG. 3 is a cross-sectional end view of a gas generant stripincorporated into an inner housing of the present invention;

FIG. 4 shows perspective views of various embodiments of gas generantstrips in accordance with the present invention;

FIG. 5 is a cross-sectional side view of a second embodiment of theinflator of the present invention;

FIG. 6 is a cross-sectional side view of a third embodiment of theinflator of the present invention;

FIG. 7 is a cross-sectional side view of a fourth embodiment of theinflator of the present invention; and

FIG. 8 is a schematic representation of an exemplary vehicle occupantrestraint system incorporating an inflator in accordance with thepresent invention.

DETAILED DESCRIPTION

FIGS. 1 and 2 show cross-sectional view of an inflator 10 in accordancewith the present invention. Inflator 10 includes an elongated outerhousing 12 and an elongated inner housing 14 positioned in an interiorof outer housing 12, thereby forming a cavity 30 between inner housing14 and outer housing 12. All the component parts of inflator 10 aremanufactured from materials and with processes known in the art.

Outer housing 12 includes a first end 70, a second end 71, and alongitudinal axis 13. Outer housing 12 has one or more orifices 22formed therealong to enable fluid communication between the interior andthe exterior of the outer housing. Orifice(s) 22 are adapted to conveygas produced by the combustion of a gas generant composition to anassociated airbag (not shown). In the embodiment shown in FIGS. 1 and 2,orifice(s) 22 are aligned along the length of outer housing 12.Orifice(s) 22 also open from the outer housing interior toward a firstside (designated “F”) of the inflator. Orifice(s) 22 may be formed asone or more longitudinal slits extending along outer housing 12, or theorifice(s) may be formed as holes spaced along outer housing 12. Outerhousing 12 may be fabricated using any one of a variety of knowprocesses, such as extrusion or roll forming. Outer housing 12 ispreferably made from a metal or metal alloy, for example, steel oraluminum. Alternatively, outer housing 12 may be made from polymers orother suitable materials.

Inner housing 14 includes a first end 74, a second end 75 opposite firstend 74, and a longitudinal axis 76. Inner housing 14 also has aninterior and one or more orifices 20 formed therealong. Orifice(s) 20are adapted to convey gas produced by the combustion of a gas generantcomposition to cavity 30. In one embodiment, orifice(s) 20 are alignedalong the length of inner housing 14. Orifice(s) 20 also open from theinner housing interior toward a second side (designated “S”) of theinflator. Orifice(s) 20 may be formed as one or more longitudinal slitsextending along inner housing 14, or the orifice(s) may be formed asholes spaced along inner housing 14. Inner housing 14 may be fabricatedusing any one of a variety of know processes, such as extrusion or rollforming. Inner housing 14 is preferably made from a metal or metalalloy, for example, steel or aluminum. Alternatively, inner housing 14may be made from polymers or other suitable materials.

In the embodiment shown in FIGS. 1 and 2, inner housing 14 is positionedcoaxial with outer housing 12. In addition, as seen in FIGS. 1 and 2,second side S of inflator 10 is opposite first side F of the inflator.The arrangement of the respective outer and inner orifices towardopposite sides of the inflator maximizes filter efficacy by forcing theinflation gas produced during inflator activation to flow out of innerhousing orifices 20, around inner housing 14, and out of inflator 10through outer housing orifices 22. In flowing from inner housingorifices 20 to outer housing orifices 22, the inflation gas streambecomes bifurcated, a portion of the stream flowing around one side ofinner housing 14, and another portion of the stream flowing around anopposite side of the inner housing, as indicated by arrows “B” of FIG.2. Positioning inner housing orifice(s) 20 opposite outer housingorifice(s) 22 provides substantially equal filtration of each portion ofthe stream, by placing outer housing orifice(s) 22 an equal distancefrom inner housing orifice(s) along either side of inner housing 14.

Referring to FIG. 3, a quantity of a gas generant composition 16 extendsalong the interior of inner housing 14. A pyrotechnic is ignitable toproduce an inflation gas for inflating an airbag (not shown) in avehicle occupant restraint system. In the embodiment shown, gas generantcomposition 16 is substantially coextensive with inner housing 14. Gasgenerant 16 has a substantially “C”-shaped cross-section with a slot 24extending along the length of the gas generant. In a preferredembodiment, opening 24 is oriented toward orifice(s) 20 in inner housing14.

The “C”-shaped cross section of gas generant 16 provides a greaterexposed gas generant surface area than would be achievable without theslot. This enhances the ignition and burning of the gas generantcomposition upon inflator activation, while also providing fluidcommunication between a relatively large surface area of gas generant 16and inner housing orifice(s) 20.

Referring to FIGS. 1 and 2, in a particular embodiment, thesubstantially “C”-shaped cross-section of gas generant 16 defines anannular wall 19 having an outer radius r_(o) and an inner radius r_(i),with slot 24 extending through wall 19. In this embodiment, the totalouter surface area A of the gas generant block of FIGS. 1 and 2 isapproximated by the relation:A=L(X(r _(o) +r _(i))+2(r _(o) −r _(i)))+X(r_(o) ² r _(i) ²)   (1)where:

-   -   L=the length of the gas generant block;    -   r_(o)=the outer radius of the wall;    -   r_(i)=the inner radius of the wall; and    -   X=an arc length occupied by the annular wall, in radians.        As a comparative example, for r_(o)=0.25 inches, r_(i)=0.15        inches, L=10 inches, and X=5/3 πradians:        A=10(5/3 π(0.25+0.15)+2(0.25−0.15))+5/3π(0.25²−0.15²)=23.15 in.²        In contrast, the surface area of a solid cylinder is given by        the relation        2πr L   (2)        where r is the radius of the cylinder and L is the length of the        cylinder. For a solid cylinder with the dimensions given above,        the surface area is 2π(0.25)(10)=15.71 in.². Thus, it may be        seen that the gas generant geometry shown in FIG. 3 provides a        larger overall surface area for a given size envelope of gas        generant than a solid cylinder would provide.

In one embodiment (shown in FIG. 4), gas generant 16 is in the form of astrip comprising a unitary, longitudinal block. By forming gas generant16 as a unitary block, greater control of the gas generant geometryinside inner housing 14 may be achieved. This results in morecontrollable and predictable gas generant combustion propagation. Easeof handling of the gas generant composition during assembly of theinflator is also promoted.

FIG. 4 shows perspective views of extruded strips of gas generant 16 a-cin accordance with the present invention. Gas generant strip 16 a is anelongate, substantially rectangular strip that may be placed in aninterior of inner housing 14 and deformed to have a substantiallyC-shaped cross section, as illustrated by strips 16 b and 16 c. Strip 16c has a more completely closed shape (i.e., a slot 24 with a smalleropening) than strip 16 b, corresponding to a relatively greater quantityof gas generant, as might be formed when incorporating and deforming arelatively larger flat strip 16 a. In alternative embodiments, the gasgenerant is extruded having the desired final cross sectional curvature,rather than being extruded as a flat strip and subsequently deformed.

In another alternative embodiment, shown in FIG. 5, gas generantcomposition 16 is in the form of a plurality of wafers 16e stackedlongitudinally along the interior of inner housing 14. Each of gasgenerant wafers 16 e has a substantially “C”-shaped cross-section with aslot 24 formed therein, as previously described. Slots 24 of individualwafers 16e are aligned longitudinally along the length of inner housing14 to provide, in combination, a slot extending along the length of thegas generant as previously described.

The combustion rate of gas generant 16 can also be affected by varyingthe L/D ratio of the gas generant, which is defined as the ratio of thegas generant length to the gas generant outer diameter. Morespecifically, a relatively longer, narrower (high L/D ratio) gasgenerant strip will bum more rapidly and evenly than a thicker strip(i.e., a strip with a larger diameter). Thus, if it is desired toincrease the amount of inflation gas generated for a particularapplication, the length of the gas generant extending along innerhousing 14 may be increased without increasing the outer diameter of thegas generant. It is believed that maintaining a ratio of length-to-outerdiameter of at least 10:1 provides rapid and efficient combustionpropagation for the applications described herein.

Gas generant composition 16 is a fast burning, relatively easilyignitable composition. In one embodiment, gas generant 16 comprisessilicone as a fuel at about 10-25% by weight; a perchlorate oxidizersuch as ammonium, lithium, or potassium perchlorate; and a strontiumsalt such as strontium nitrate or strontium carbonate as a coolant. Theoxidizer and coolant typically comprise about 75-90% by weight of thepropellant. The silicone may be purchased, for example, from GeneralElectric or other well-known suppliers. Silicone provides the additionalbenefit of acting as a binder, facilitating the extrusion of gasgenerant strips or ribbons, as described herein. The other gas generantconstituents may be provided by suppliers or by manufacturing methodswell known in the art. Exemplary suitable compositions are disclosed inU.S. patent application Publication No. 2001/0045735, Ser. No.09/846,004, incorporated by reference herein.

In alternative embodiments, the gas generant composition can be made toincorporate fast burning and slow burning compositions, with the fastburning portion on the inside surface of the extrusion, as installedinto inner housing 14. The fast burning composition supports theignition mechanism and produces the gas necessary for initial airbaginflation. The slow burning composition is ignited by the fast burninglayer and provides a relatively slow generation of gas necessary forlong term inflation applications, such as roll-over airbags.

Referring again to FIGS. 1 and 2, a metallic mesh filter 15 ispositioned in the cavity formed between outer housing 12 and innerhousing 14, between inner housing orifice(s) 20 and outer housingorifice(s), for filtering particulate materials produced during inflatoractivation, as well as serving as a heat sink for hot inflation gases.Suitable metallic mesh is readily obtainable from suppliers such asWayne Wire, Inc., of Kalkaska, Mich.

Referring to FIG. 2, an igniter 40 operatively coupled to gas generantcomposition 16 so as to enable fluid communication between the igniterand the gas generant composition upon activation of the inflator. In theembodiment shown, igniter 40 is coupled to an end of inner housing 14.Igniter 40 may be formed as known in the art. One exemplary igniterconstruction is described in U.S. Pat. No. 6,009,809, incorporatedherein by reference.

Igniter 40 is coupled to the inflator structure in a manner designed tominimize inflation gas pressure loss through the igniter end of theinflator upon activation of the inflator. Referring to FIG. 2A, in apreferred embodiment, igniter 40 is incorporated within an igniterassembly 39 secured within outer housing 12. Igniter assembly 39includes an outer sleeve 41, igniter 40, and an igniter insert 42. Outersleeve 41 defines a rear cavity 41 a for receiving a mating interconnector other suitable electrical interface for connection to igniterterminals 40 a. Outer sleeve 41 also includes an annular wall 41 bdefining a front cavity 41 c and an orifice 41 d enclosed by wall 41 bfor receiving igniter 40 and igniter insert 42 therein. An inner surface41 b-1 of annular wall 41 b is threaded for mating engagement withcomplementary threads formed along an outer surface of igniter insert42, as described below.

Igniter insert 42 includes an orifice 42 a extending through a centralportion of the insert for receiving a portion of igniter 40 therein. Anannular wall 42 b encloses orifice 42 a. An outer surface of annularwall 42 b is threaded for mating engagement with complementary threadsformed along inner surface 41 b-1 of outer sleeve 41, as previouslydescribed.

Igniter 40 may be inserted into outer sleeve orifice 41 d and secured inouter sleeve 41 using one of a number of known methods, such ascrimping, adhesive application, forming of an interference fit, etc.When igniter 40 is secured within outer sleeve 41, igniter insert 42 isscrewed into outer sleeve front cavity 41 c. It is believed thatthreaded engagement between igniter insert 42 and outer sleeve 41minimizes inflation gas pressure loss through the interface betweenigniter insert 42 and outer sleeve 41.

Additional seals may be formed at interfaces between the igniterassembly components and between igniter assembly 39 and other componentsof the inflator. In one embodiment, shown in detail in FIG. 2A, annularcavities for accommodating O-ring seals 43 are provided in outer sleeve41 and igniter insert 42, adjacent the interfaces between inner housing14 and igniter insert 42, between filter 15 igniter insert 42, betweenfilter and outer sleeve 41, and between outer housing 12 and outersleeve 41. These seals aid in minimizing pressure losses from theinflator. Igniter assembly 39 may then be secured within outer housing12 by, for example, an interference fit formed between the outer housingand outer sleeve 41. An end portion of outer housing 12 is then crimpedover outer sleeve 41 to secure the outer sleeve within the outerhousing.

Operation of the inflator will now be discussed with reference to FIGS.1 and 2.

Upon a crash event, a signal from a crash sensor (not shown) is conveyedto igniter 40, thereby activating the igniter and igniting gas generant16. Upon activation of igniter 40, ignition of the gas generant 16progresses rapidly from inner housing end 74 toward inner housing end75. A pressure wave produced by igniter 40 progresses down the length ofthe inside surface of gas generant 16, igniting the propellant as itpasses. The gas generant ignites rapidly, feeding the pressure wave. Byutilizing a gas generant having the disclosed composition and shape, anignition cord is not required, as in certain known designs. Moreover,the substantially C-shaped cross section of gas generant 16 provides fora relatively smooth ignition of the gas generant. Due to the pressuresensitivity of some propellants, this shape imparts considerableadvantages. Inflation gas produced by combustion of gas generant 16proceeds out of inner housing orifice(s) 20 and flows around either sideof inner housing 14 and also through filter 15. The inflation gas thenexits the inflator via outer housing orifice(s) 22. Arrows “B” in FIG. 1illustrate an approximate direction of gas flow upon inflatoractivation.

In other alternative embodiments, flow of inflation gases may also bedirected axially (along the longitudinal axis of the inflator) as wellas radially outward from the inflator. This enables portions of certainairbag configurations to be filled more rapidly than would be the casewith purely radial inflation gas flow. FIGS. 6 and 7 show embodiments ofinflators in accordance with the present invention that incorporate anaxial flow component.

Referring to FIG. 6, in one embodiment, inner housing 14 includes anaperture 80 formed in first end 74 of the housing. Similarly, outerhousing 12 includes an aperture 82 formed in first end 70 of outerhousing 12. A filter 90 is positioned intermediate inner housing firstend aperture 80 and outer housing first end aperture 82 for filteringcombustion products generated by combustion of gas generant composition16 within inner housing 14. Upon activation of the inflator, inflationgases generated by combustion of gas generant composition 16 flow frominner housing first end aperture 80 through filter 90 to exit outerhousing first end aperture 82, and into an associated airbag (notshown).

FIG. 7 shows another embodiment of the inflator in which inflation gasesgenerated in inner housing 14 flow out of both ends of the inflator, aswell as radially out of the inflator. In this embodiment, an additionalaperture 83 is formed in second end 75 of inner housing 14, and anadditional aperture 85 is formed in second end 71 of outer housing 12.Another filter 92 is positioned intermediate inner housing second endaperture 83 and outer housing second end aperture 85 for filteringcombustion products generated by combustion of the gas generantcomposition. Upon activation of the inflator, inflation gases generatedby combustion of gas generant composition 16 flow from inner housingsecond end aperture 83 through filter 92 to exit the inflator via outerhousing second end aperture 85. Igniter 40 is positioned intermediateinner housing first end 74 and inner housing second end 75,approximately at a midpoint of the gas generant, so that combustionpropagation of gas generant 16 proceeds toward either end of innerhousing 14 and finishes substantially simultaneously.

Referring now to FIG. 8, any of the Inflator embodiments described abovemay also be incorporated into an airbag system 200. Airbag system 200includes at least one airbag 202 and an inflator 10 coupled to airbag202 so as to enable fluid communication with an interior of the airbag.As described above, inflator 10 incorporates a longitudinal gas generantarrangement 16 comprising a unitary, longitudinal block having a slot 24extending along a length thereof and a substantially “C”-shapedcross-section, a housing structure enclosing gas generant strip 16, andan igniter 40 operatively coupled to gas generant strip 16 so as toenable fluid communication between igniter 40 and gas generant strip 16upon activation of the inflator. Airbag system 200 may also be incommunication with a crash event sensor 210 including a known crashsensor algorithm that signals actuation of airbag system 200 via, forexample, activation of airbag inflator 204 in the event of a collision.

Referring again to FIG. 8, airbag system 200 may also be incorporatedinto a broader, more comprehensive vehicle occupant restraint system 180including additional elements such as a safety belt assembly 150. FIG. 8shows a schematic diagram of one exemplary embodiment of such arestraint system.

Safety belt assembly 150 includes a safety belt housing 152 and a safetybelt 10 in accordance with the present invention extending from housing152. A safety belt retractor mechanism 154 (for example, a spring-loadedmechanism) may be coupled to an end portion 153 of the belt. Inaddition, a safety belt pretensioner 156 may be coupled to beltretractor mechanism 154 to actuate the retractor mechanism in the eventof a collision. Typical seat belt retractor mechanisms which may be usedin conjunction with the safety belt embodiments of the present inventionare described in U.S. Pat. Nos. 5,743,480, 5,553,803, 5,667,161,5,451,008, 4,558,832 and 4,597,546, incorporated herein by reference.Illustrative examples of typical pretensioners with which the safetybelt embodiments of the present invention may be combined are describedin U.S. Pat. Nos. 6,505,790 and 6,419,177, incorporated herein byreference.

Safety belt system 150 may be in communication with a crash event sensor158 (for example, an inertia sensor or an accelerometer) including aknown crash sensor algorithm that signals actuation of belt pretensioner156 via, for example, activation of a pyrotechnic igniter (not shown)incorporated into the pretensioner. U.S. Pat. Nos. 6,505,790 and6,419,177, previously incorporated herein by reference, provideillustrative examples of pretensioners actuated in such a manner.

It is contemplated that the present invention will find primaryapplication in side impact or head curtain airbag systems; however, itis not limited thereto. It will also be understood that the foregoingdescription of an embodiment of the present invention is forillustrative purposes only. As such, the various structural andoperational features herein disclosed are susceptible to a number ofmodifications commensurate with the abilities of one of ordinary skillin the art, none of which departs from the scope of the presentinvention as defined in the appended claims.

1. An inflator comprising: an elongated outer housing having an interiorand at least one orifice to enable fluid communication between the outerhousing interior and an exterior of the outer housing, the at least oneouter housing orifice opening from the outer housing interior toward afirst side of the inflator; an elongated inner housing positioned in theouter housing interior, the inner housing having an interior and atleast one orifice to enable fluid communication between the innerhousing interior and an exterior of the inner housing, the at least oneinner housing orifice opening from the inner housing interior toward asecond side of the inflator, a quantity of a gas generant compositionextending along at least a portion of the interior of the inner housing,the gas generant having a length and a substantially “C”-shapedcross-section with a slot extending along the length of the gasgenerant; and an igniter operatively coupled to the gas generantcomposition, thereby initiating combustion of the gas generantcomposition upon activation of the inflator.
 2. The inflator of claim 1wherein the gas generant composition is formed into a unitary block. 3.The inflator of claim 1 wherein the inner housing has a longitudinalaxis and the gas generant composition comprises a plurality of wafersstacked along the longitudinal axis.
 4. The inflator of claim 1 whereinthe inner housing is positioned coaxial with the outer housing.
 5. Theinflator of claim 1 wherein the substantially “C”-shaped cross-sectiondefines an annular wall having an outer radius and an inner radius, andwherein the slot extends through the wall.
 6. The inflator of claim 5wherein the gas generant has an outer diameter and a ratio oflength-to-outer diameter of at least 10:1.
 7. The inflator of claim 1wherein the second side of the inflator is opposite the first side ofthe inflator.
 8. The inflator of claim 1 wherein the gas generantcomposition is substantially coextensive with the inner housing.
 9. Theinflator of claim 1 wherein the slot is in communication with the atleast one inner housing orifice.
 10. The inflator of claim 1 wherein theinner housing includes a first end, a second end opposite the first end,and an aperture formed in the inner housing first end; the outer housingincludes a first end proximate the inner housing first end, a second endproximate the inner housing second end, and an aperture formed in theouter housing first end; and a second filter is positioned intermediatethe inner housing first end aperture and the outer housing first endaperture for filtering combustion products generated by combustion ofthe gas generant composition whereby, subsequent to activation of theinflator, inflation gases generated by combustion of the gas generantcomposition flow from the inner housing first end aperture through thesecond filter to exit the outer housing first end aperture.
 11. Theinflator of claim 10 further including an aperture formed in the secondend of the inner housing, an aperture formed in the second end of theouter housing, and a third filter positioned intermediate the innerhousing second end aperture and the outer housing second end aperturefor filtering combustion products generated by combustion of the gasgenerant composition whereby, subsequent to activation of the inflator,inflation gases generated by combustion of the gas generant compositionflow from the inner housing second end aperture through the third filterto exit the outer housing second end aperture.
 12. The inflator of claim11 wherein the igniter is positioned intermediate the inner housingfirst end and the inner housing second end.
 13. The inflator of claim 10wherein the igniter is positioned proximate the second end of the innerhousing.
 14. The inflator of claim 1 further comprising a filterpositioned intermediate the at least one inner housing orifice and theat least one outer housing orifice for filtering combustion productsgenerated by combustion of the gas generant composition.
 15. Theinflator of claim 1, wherein a direction of flow of inflation gasexiting the at least one outer housing orifice is angularly spaced apartapproximately 180 degrees from a direction of flow of inflation gasexiting the at least one inner housing orifice.
 16. The inflator ofclaim 1 wherein the igniter is threadedly received within the outerhousing
 17. An airbag system comprising the inflator of claim 1 and atleast one airbag coupled to the inflator airbag thereby providing fluidcommunication between the inflator and an interior of the airbag uponactivation of the inflator.
 18. The airbag system of claim 17 whereinthe inflator comprises: an inner housing enclosing the gas generantstrip, the inner housing having at least one orifice to enable fluidcommunication between the gas generant strip and an exterior of theinner housing; an outer housing enclosing the inner housing to form acavity therebetween, the outer housing having at least one orifice toenable fluid communication between the inner housing and an exterior ofthe outer housing; and a filter positioned in the cavity for filteringcombustion products generated by combustion of the gas generant strip.19. The airbag system of claim 18 further comprising a crash eventsensor in communication with the igniter, the crash event sensorincluding a known crash sensor algorithm that signals activation of theairbag system in the event of a collision.
 20. The airbag system ofclaim 17 wherein the at least one airbag is a side curtain airbag. 21.The airbag system of claim 17 wherein the at least one airbag is a headcurtain airbag.
 22. A vehicle occupant restraint system including theinflator of claim
 1. 23. The inflator of claim 1 wherein the gasgenerant composition is a gas generant strip comprising a unitary,longitudinal block having a slot extending along a length thereof, and asubstantially “C”-shaped cross-section.
 24. A vehicle occupant restraintsystem comprising an airbag system having at least one airbag and aninflator coupled to the airbag so as to enable fluid communication withan interior of the airbag upon activation of the inflator, the inflatorcomprising: a gas generant strip comprising a unitary, longitudinalblock having a slot extending along a length thereof, and asubstantially “C”-shaped cross-section; a housing structure enclosingthe gas generant strip; and an igniter operatively coupled to the gasgenerant strip so as to enable fluid communication between the igniterand the gas generant strip upon activation of the inflator.
 25. Thevehicle occupant restraint system of claim 24 further comprising asafety belt assembly including a housing and a safety belt extendingfrom the housing.
 26. The vehicle occupant restraint system of claim 24wherein the housing structure comprises: an inner housing enclosing thegas generant strip, the inner housing having at least one orifice toenable fluid communication between the gas generant strip and anexterior of the inner housing; an outer housing enclosing the innerhousing to form a cavity therebetween, the outer housing having at leastone orifice to enable fluid communication between the inner housing andan exterior of the outer housing; and a filter positioned in the cavityfor filtering combustion products generated by combustion of the gasgenerant strip.
 27. The vehicle occupant restraint system of claim 24further comprising a crash event sensor in communication with the airbagsystem, the crash event sensor including a crash sensor algorithm thatsignals activation of the airbag system in the event of a collision. 28.A gas generant strip for use in an inflator, comprising a unitary,longitudinal block having a slot extending along a length thereof, and asubstantially “C”-shaped cross-section.
 29. The gas generant strip ofclaim 28 wherein the “C”-shaped cross-section defines an annular wallhaving an outer radius and an inner radius, and wherein the slot isformed through the wall.
 30. The gas generant strip of claim 29 whereina total outer surface area A of the gas generant block is approximatedby the relation:A=L(X(r _(o) +r _(i))+2(r _(o) −r _(i)))+X(r _(o) ² −r _(i) ²) where:L=the length of the gas generant block; r_(o)=the outer radius of thewall; r_(i)=the inner radius of the wall; and X=an arc length occupiedby the wall, in radians.